Over the last several years we have developed a technology to optically generate ultrasound using laser pulses absorbed in thin polymer films. This approach produces ultrasonic intensity comparable to piezoelectric counterparts and is especially attractive for high-frequency applications. We have also developed a complementary technology for sensitive ultrasonic detection using resonant optical detectors. High-frequency ultrasound incident on these devices modulates the resonance condition and alters the intensity of a continuous wave (CW) laser beam probing the structure. The fundamental hypothesis of this proposal is that these technologies will produce very small, all-optical ultrasonic transducers enabling high spatial resolution imaging. Therefore, the primary goal of the research program described in this application is to develop a new intravascular imaging technology embedding a miniature, high-resolution ultrasonic imaging array within the tip of a guidewire used to deliver therapeutic catheters (typically 0.35 mm in diameter). A guidewire-based ultrasonic bio-microscopy (UBM) system would combine high resolution ultrasound imaging with conventional X-ray fluoroscopy in the baseline catheterization system. A wide range of technical and scientific issues must be investigated to fully exploit the capabilities of optoacoustic transduction. Therefore, it is the further aim of this application to address the following issues. 1.) Optimize optically absorbing polymer structures for efficient ultrasonic generation from 1-100 MHz. Particular emphasis will be placed on constructing optoacoustic transducers that can operate as arrays at these frequencies. 2.) Optimize polymer etalons for sensitive optical detection of ultrasound from 1-100 MHz. Particular emphasis will be placed on constructing etalons that can operate as arrays over these frequencies. 3.) Design, construct, and optimize a single element optoacoustic microscopy transducer. This device will serve as a test vehicle for all-optical ultrasonic transducers. In addition, it will be integrated into a high-performance UBM system for ophthalmology and dermatology applications. 4.) Design, construct, and optimize an all-optical, high-frequency ultrasonic array for UBM. This device will serve as a test vehicle for optical integration technologies. In addition, it will represent a significant advance for UBM by enabling real-time 3-D imaging. 5.) Design, construct, and optimize an all-optical, high-frequency ultrasonic array with dimensions that can fit within a conventional guidewire to guide coronary artery interventions.